Permanent Magnet Synchronous Motors (PMSM) have growing adoption in consumer and industrial motor applications due to their higher reliability and smaller size compared to other motors. To achieve high efficiency and low vibration and acoustic noise, Field Oriented Control (FOC) schemes are increasingly being used in consumer and industrial PMSM control for fans, pumps, compressors, geared motors, and so forth.
For highly dynamic loading (e.g., motors for electric propulsion, compressors, etc.), a fast and accurate FOC control loop can be used to control motor currents and voltages to maintain maximum efficiency. On the other hand, existing FOC schemes often have complex transformations in the critical control loop, which can make them inaccurate and relatively slow.
To further improve efficiency at the lowest cost, increasingly more control functions (e.g., digital power conversion, digital Power Factor Correction (PFC), FOC control of multiple motors, etc.) are often handled by fewer microcontrollers. New microcontrollers also include increasingly more features and peripherals (e.g., Human Machine Interfaces, communications, etc.) in order to excel in the intensely fierce market competition. However, existing FOC control strategies can be complicated and processor-intensive, tending to overburden the microcontrollers and impeding microcontroller power from being allocated to complex system functions efficiently, and hindering the full usage of microcontroller potential and features.
Existing rotor position and speed estimators for sensorless FOC include a flux estimator, a PLL estimator, Sliding-Mode Observer (SMO), and so forth. All of these can be sensitive to motor stator resistance R, and the fluctuating stator resistance (mainly due to temperature changes) can cause unpredictable errors to the estimated rotor position and speed, causing the control to become unstable particularly at low motor speed. Furthermore, with imprecise position and speed information in sensorless FOC, the stator flux and rotor flux may not always be perpendicular to each other and consequently the energy efficiency may not be maximized all the time. Some techniques have been proposed to compensate the stator resistance variations, such as online stator resistance re-estimation/tracking/recalibration and stator resistance adaptation in sensorless PMSM drives, but they can be complex and consume more resources, including processor time.